Thunberg and about 1,500 protesters, many of them schoolchildren, marched and chanted near the White House on Friday. They are calling for immediate action from the world's governments to halt global warming, reduce fossil fuel consumption and avert environmental catastrophe.

"You can't breathe money, you can't drink oil," they chanted.

Thunberg, 16, gained international attention by inspiring a series of protests and school strikes. Her activism has drawn a passionate following of children essentially challenging their elders to take action. For veteran environmental activists, that means renewed media attention and a fresh wave of passionate young volunteers pushing for change.

"What Greta has brought is a unified international presence for youth," said Natalie Mebane, policy director for the environmental group 350.org, which helped organize Friday's protest. "She's created an international youth voice."

Last month, Thunberg crossed the Atlantic Ocean in a solar-powered boat, landing in New York City on Aug. 28. She is in Washington, D.C., for several days of rallies and lobbying efforts in advance of a global climate strike declared for Sept. 20 to kick off a week of activism.

Thunberg will address the U.N. Climate Action Summit in New York on Sept. 23.